The subject matter disclosed herein relates generally to light curtains and photoelectric barriers and, more specifically, to safety light curtains for monitoring a protective field. In particular, the present invention relates to a transceiver element for an optical unit of a photoelectric barrier and to such a photoelectric barrier.
Generally, photoelectric barriers, also referred to as light curtains or light grids, detect the movement or intrusion of objects into guarded zones, and more particularly, provide protection for human operators who are working with machines or other industrial equipment. Such photoelectric barriers can be formed by two or more optical units (also called bars, sticks, edges or strips), or by one optical unit interacting with a reflective component.
Light curtains employing infrared or visible light beams are used to provide operator safety in a variety of industrial applications. Light curtains typically are employed for operator protection around machinery, such as punch presses, brakes, molding machines, automatic assembly equipment, coil winding machinery, robot operation, casting operations and the like. Conventional light curtains typically employ light emitting diodes (LED) mounted at spaced positions along a transmitter bar at one side of the guard zone and phototransistors (PT), photodiodes or photoreceivers mounted along a receiver bar at the opposite side of the zone. The LEDs transmit modulated infrared light beams along separate parallel channels to the PTs at the receiver bar. If one or more beams are blocked by an opaque object, such as the operator's arm, a control circuit shuts the machine down, prevents the machine from cycling, or otherwise safeguards the area.
Usually, safety light curtains comprise two optical units, which are formed as two different constructional units, one of the optical units having the functionality of an emitter and one of a receiver. This dedicated architecture of an emitter and receiver, however, has several drawbacks.
Firstly, the fabrication costs are high, because each type of optical unit has to be fabricated differently. Further, due to the fact that the optical communication is only unidirectional, for example, from the sender to the receiver, the optical synchronization may be difficult and a transmission of communication information is possible only in one direction.
It has already been proposed to locate receivers and transmitters on each of the first and second optical units, as this is described in the European patent EP 1870734 B1. Here, the light curtain has two identical transmitting/receiving strips, to which transmitting and receiving units are fixed. The transmitting/receiving strips are placed opposite to each other with a protective field being formed between the strips. The transmitting/receiving strips are identically formed in control and evaluation units. The control and evaluation units have safety outputs, which are formed together as a switching channel. An identical power supply is provided for all the strips.
Furthermore, it is known from EP 2511737 A1 to provide a modular light curtain and optical unit for such a light curtain.
Most standard concepts use integrated circuits which are either dedicated to drive radiation emitters or to evaluate the signals from radiation receivers. Hence, for a transceiver element having emitters and receivers, either two different control elements are required or each of them has a part that is not used for the specific task, thus generating unnecessary costs.
Thus it would be desirable to overcome the above mentioned problems and to provide a transceiver element for use in photoelectric barriers that allows for a high flexibility and reliability and can be fabricated in a cost-effective way.